Characteristics of a-Si thin-film transistors with an inorganic black matrix on the top

The characteristics of a-Si bottom-gate TFT test devices with several kinds of inorganic "quasi-black matrix," such as metal, semiconductor, and insulator, on the top were investigated for various black matrix (BM) resistivities. In the I_d-V_g characteristics, for a BM sheet resistance of about ∼1 × 10¹² Ω/□, a high off current and large V_th shift were observed due to the back-gating effects when the BM is charged up. According to the ac dynamic characteristics, there was almost no leakage due to the capacitive coupling between source and drain after 16.6 msec (one frame) when the BM sheet resistance was above ∼7× 10¹³Ω/□ It was found that hydrogenated amorphous silicon germanium (a-SiGe:H) film, which has enough optical density, with the sheet resistance above the order of 10¹⁴Ω/□ is a promising candidate for an inorganic BM on TFT array.